The Study of Osteoporotic Fractures (SOF) is a cohort of 10,366 women who were greater than or equal to 65 years old at enrollment in 1986-7. During 18 years and 8 examinations, SOF has developed a comprehensive array of phenotypic data, along with archives of 53,000 biological specimens and 67,500 radiographs. Findings from SOF, reported in 235 papers, have shaped clinical practice and guidelines for fracture prevention, and advanced the understanding of cognitive function, breast cancer, osteoarthritis, and other age-related conditions. SOF continues to be very productive, with 93 publications since our last renewal in 2000, including 60 articles from 45 external, and mostly junior, investigators. All SOF data are now available publicly via SOF Online. We propose to sustain, build, and produce important discoveries from these unique SOF resources. The SOF cohort has become one of the largest, longest, and best characterized cohorts of women in the 9th and 10th decades of life, the fastest growing segment of the US population. In addition to data about risk factors, bone mass, and fractures, we have nearly two decades of serial assessments of lower extremity function, cognitive function, and falls. In a Year 20 Exam, we will examine surviving SOF participants in clinic or home to expand our assessment of cognitive function with new dimensions and assess lower extremity function using the standardized and validated Short Physical Performance Battery. These examinations will allow us to analyze why some women have excellent cognitive function and lower extremity function so late in life. We will use blood stored from our Year 10 Exam to test the hypotheses that excellent renal function, low levels of inflammation, and normal levels of 25(OH)Vitamin D are associated with maintaining and achieving excellent lower extremity function, high cognitive function, a low risk of falls, and a low risk of hip fracture into the 9th and 10th decades of life. Potential public health impacts: While the oldest old women are the fastest growing segment of the US population, little is known about how to maintain their independence. Renal function, inflammation, and vitamin D levels are modifiable. If our hypotheses are born out, this may lead to trials and recommendations about lifestyle, vitamin D supplementation, or medication, to promote high levels of function late in life.